Embodiments of the disclosed technology relate to a thin film transistor and a manufacturing method thereof.
Recently, the panel display technology is undergoing a rapidly development. Performance of thin film transistor (TFT) which is used as an elementary element of a driving circuit of an active matrix display device is continuously improved. Compared with traditional amorphous silicon TFT, low temperature polycrystalline silicon (LTPS) TFT is advantageous due to its high electron mobility, low threshold voltage and so on. Therefore, compared with the driving circuit constituted with the traditional amorphous silicon TFTs, the driving circuit constituted by LTPS TFTs exhibits higher speed and lower power consumption.
The active region of a LTPS TFT is formed by a LTPS thin film. Generally, the LTPS thin film is formed by annealing an amorphous silicon thin film. An N-type LTPS TFT and a P-type LTPS TFT, which are formed by such the poly-crystallization technology, have different threshold voltages. The absolute value of the threshold voltage of a P-type LTPS TFT is generally larger than that of an N-type LTPS TFT. When complementary metal oxide semiconductor (CMOS) devices constituted with such LTPS TFTs are used in the peripheral driving circuit of an active matrix display device, the driving circuit used for this device becomes complicated, due to the asymmetry of the threshold voltages of the P-type LTPS TFT and the N-type LTPS TFT.
In order to eliminate the threshold voltage asymmetry between the P-type LTPS TFT and the N-type LTPS TFT in a CMOS device, an existing technology provides a method for ion-doping channels of the N-type LTPS TFTs or the P-type LTPS TFTs (channel doping), in which an ion-implantation process is performed on the channels of the LTPS TFTs to change the energy band structure of the channels and therefore the threshold voltages.